It should be understood that the term "inks", within the meaning of the present invention, also includes India inks of all types containing binding agent and/or pigments, in so far as they meet the stipulated requirements and fulfill the other conditions of the proposed embodiment.
Known from the German patent 27 24 820 B2 are "A Method and Working Means for Producing Colored Stroke Applications on a Document", whose color effect is changed by aftertreatment, after applying the ink on the document. According to that reference, the aftertreatment should be effected through chemical means with the assistance of a bleaching liquor, by which one of several colorants contained in the coloring agent is converted into its leuco form, so that only the other colorant then remains visible in its original color in the stroke application.
Thus, in that case, a color change in the stroke application is always effected on the basis of chemical reactions or changes within a coloring-agent component in the stroke application. If and to what extent color changes in the stroke application are also present or possible in that case, without any chemical aftertreatment and/or under temperature influences, is not discernible.
Moreover, also known are inks or India inks, in whose stroke applications a chemical reaction is triggered in response to exceeding a certain temperature, the reaction producing a color change in the stroke application. In those cases, the color change takes place because of a pH-value change of certain colorants having indicator effect. The disadvantage of such ink compositions is that special indicator colorants are needed, and that the color contrast before and after the color change is usually only very slight and poorly visible. Furthermore, the expenditure for producing such inks, which in part also act in a very corrosive manner, is high.
None of the known inks or India inks appears capable of clearly indicating specific treatment conditions or treatment methods of objects marked or labeled by them. In particular, it is not possible to indicate, for example, heating having been effected as part of a sterilization processes.
Therefore, an object of the present invention is to produce an ink or India ink for use in manual writing devices or in writing and drawing equipment, such as in continuous ink-jet equipment, which does not have the disadvantages mentioned, and whose stroke applications are capable of making known or indicating, without chemical means or aftertreatments, specific treatment conditions or treatment methods of objects marked or labeled by them.